The operating life of electrical equipment such as transformers depends to a large extent upon the dielectric properties of the transformer wire insulation. When the coating ceases to provide sufficient insulation between the turns of the transformer coil, electrical breakdown can occur between the turns causing the transformer to fail. Long term dielectric failure can be caused by the hydrolysis of the wire insulation at the temperatures incurred during transformer operation. The primary source of water contributing to the hydrolysis reaction is the thermal degradation of the cellulosic composition of the transformer winding insulation paper.
Besides having good thermal aging properties, the insulated wire must be tough and sufficiently flexible to be wound into a transformer coil without cracking in order to maintain its insulating properties. Transformer wire insulation such as those described within U.S. patent applications Ser. Nos. 889,889, and 970,249 are continuously being subjected to improvements in order to obtain better electrical, physical and thermal properties.
In order to provide insulating coating systems which have improved properties, a plurality of different types of catalysts were employed to cure the polyvinyl acetal, phenolic and epoxy resins within the coating composition. The investigation of the effects of various catalysts upon the coated transformer wire properties showed that the catalysts affect the thermal stability of the coated transformer wire when subjected to accelerated thermal aging tests.
The purpose of this disclosure is to provide a wire coating enamel composition having a preferred catalyst for promoting good flexibility and improved hydrolytic stability.